<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>map</title>
</head>
<body>
    <script>
        let arr = [1,2,3,4];

        // map 数组中的一个方法, 接收一个回调函数, 
        let result = arr.map((item, index) => {
            console.log(index);
            return item * 10;
        });

        // let result = arr.map(item => item * item);

        console.log(result);

    </script>
</body>
</html>